This invention relates to an internal combustion engine and method of operating such engine so as to improve performance.
As is well known, internal combustion engines in most applications are called upon to run over a wide variety of speed and load ranges. This is particularly true when the engine is used in an automotive application. In connection with spark ignited engines, a distributor and advance mechanism is provided for firing the spark plugs at a pre-determined timing in relation to the crank or output shaft angle. As with many components of the engine and its design, the chosen point of spark firing at a given speed and/or load condition is a comprise dictated by the difficulty and cost of providing optimum timing at all conditions. As a result, performance with conventional engines suffers under at least some of these running conditions.
Conventional distributors, which may be of either the contact point or solid state type embody both governor and vacuum advance devices. The governor advance provides spark timing in relation to engine speed while the vacuum advance mechanism compensates to some extent the changes in load. Of course, the use of such combined advance mechanisms compensates the structure, adds to its cost and introduces the possibility of unreliability. Further, even the use of these two advance mechanisms does not provide the appropriate or necessary degree of control.
As a specific example of this problem, the distributors used with conventional engines provide something less than optimum advance characteristics at idle and low load conditions. With conventional engines, the rate of flame propogation in the combustion chamber is extremely low under idling. Thus, to insure complete combustion and smooth and efficient running considerable spark advance should be employed at idle. However, if a high degree of initial advance at idle is provided, the likelihood of pre-ignition at higher load and speed ranges is greatly increased. Thus, it has been the practice to provide a substantially reduced spark advance at idle so as to reduce the likelihood of pre-ignition at higher speeds and load ranges. Furthermore, it has been the practice recently to severely retard the idle spark advance (even after top dead center T.D.C.) to attempt to control the amount of nitrous oxide in the exhaust gas. Of course, this provides extremely inefficient low speed operation as well as introducing the likelihood of extremely rough running.
It is, therefore, a principle object of this invention to provide an internal combustion engine and method of operating it which controls the rate of combustion under specified load and/or speed ranges so as to permit a simpler spark advance mechanism and at the same time provide better control of this characteristic.
As has been previously noted, it has been the practice to provide both vacuum and governor advance mechanisms with conventional distributors in an effort to obtain more accurate control under all running conditions. It is another object of this invention to provide a distributor spark advance mechanism which permits varying spark advance characteristics without necessitating the incorporation of a vacuum advance mechanism.